Vehicle child seats, as are used for securing children in passenger vehicles, for example, are generally known. For securing the child in the child seat, either the belt system of the vehicle itself or an integrated child seat belt system is used. The child seat is positioned in the vehicle either directly onto the vehicle seat or indirectly onto a child seat base fastened in the vehicle, as is disclosed for example in DE 10 2006 011 520 A1. The fastening of the child seat and optionally of the child seat base in the vehicle takes place by means of the vehicle belt or a fastening system known by the term ISOFIX.
Belt tensioners for adult occupants of passenger motor vehicles are included in so-called passive safety systems. Belt tensioners tension the safety belts immediately before or during an accident. By tensioning the belt and the resulting tighter bearing of the belt against the body of the occupant, said occupant participates at an early stage in the deceleration of the vehicle and slipping down through the lap belt is prevented. In order to limit the forces produced on the occupant by means of the belt system, the belt tensioners may be combined with so-called belt force limiters which, from a defined belt force, for example, produce a specific unwinding of the belt strap from a belt retractor.
An optimal retaining action of a child in a vehicle child seat with an integrated belt system also requires the belt to bear as tightly as possible against the body. Thus it is also advantageous to incorporate the belt tensioning function in a child seat.
A vehicle child seat is disclosed in DE 197 22 096 A1 which has a retaining device consisting of an integrated belt system and belt tensioner arrangement. For triggering the belt tensioning function of the child seat, a sensor device as well as a control unit are required, of which at least the control unit is integrated outside the child seat in a fixed manner in the vehicle. When mounting the child seat in the vehicle, therefore, said child seat has to be attached by means of releasable plug connections to the control unit of the vehicle. If this inadvertently does not take place, the belt tensioning arrangement is inoperational. This fault is intended to be eliminated by additional monitoring means.
DE 102 51 040 A1 discloses a coupling device between the belt tensioning system of the vehicle itself and the belt system integrated in the child seat. A separate belt tensioning device is not provided in the child seat. The optimal retaining action of the child seat belt system is thus dependent on the presence of a belt tensioner in the vehicle. This is frequently not the case, however, in particular with rear seats of passenger motor vehicles, so that the use of the child seat remains restricted to specific vehicle models and/or to the front seats.
A vehicle child seat is disclosed in US 2007/0228787 A1 for directly fastening to a vehicle seat, comprising a backrest, a seat surface, an integrated belt system (10) for fastening a child in the vehicle child seat and a belt tensioning device comprising a trigger sensor, an energy storage device and a tensioning mechanism which, when exceeding a defined force acting on the vehicle child seat, in particular a crash force, abruptly tensions the belt system.
DE 20 2005 013 257 U1 discloses a belt force limiting function according to which, in the event of a crash and when exceeding a limit force, the belt is lengthened in a damped manner. A belt tensioner is not provided in this case.